Medical procedures utilizing interventional instruments (e.g., endoscopes) inserted through the skin often require preservation of the access path after the instrument is withdrawn from the body. Typically, these procedures require insertion of a sheath into the body along a guidewire previously coupled to the interventional instrument. The sheath prevents the tract established by the interventional device from closing or collapsing. One example procedure involves insertion of a dilation catheter and a guidewire along the nephrostomy tract. Once properly positioned in the body, a balloon near the distal end of the catheter is inflated to dilate the tract. A sheath is then advanced through the nephrostomy tract before the tract substantially collapses.
This procedure has inherent problems. The sheath is typically radiopaque, thus the physician cannot observe objects within or obstructed by the sheath by standard fluoroscopic techniques. In addition, optical imaging devices inserted through the sheath are unable to look out radially, thus prohibiting accurate location of objects adjacent to the sheath. Moreover, the guidewire may migrate during the exchange of instruments through the sheath, thus inhibiting placement of additional instruments along the tract.